The invention relates to an axle for wheels of a two-track (or double-tracked) motor vehicle, wherein the axle has, on each side of the vehicle, a wheel carrier, a damper strut, a transverse link and a transverse leaf spring which imparts an at least partial wheel-controlling action laterally and/or in a vehicle longitudinal direction. The damper strut has a damper tube and a damper piston which is movable in the damper tube along a damper longitudinal axis. The damper strut is attached by the damper tube to the wheel carrier and is supported at a first effective kinematic point on the wheel carrier. The transverse link has a wheel-carrier-side end region and is attached by the wheel-carrier-side end region to the wheel carrier and is supported at a second effective kinematic point on the wheel carrier. With regard to a functionally installed state of the axle in a two-track motor vehicle, the transverse leaf spring extends substantially in a vehicle transverse direction and has at least one wheel-carrier-side end region.
Axles for two-track motor vehicles with transverse leaf springs, that is to say with leaf springs running substantially in a vehicle transverse direction, in particular with transverse leaf springs whose spring leaves are, with regard to a functionally installed state in a vehicle, arranged one above the other in a vehicle vertical direction are generally known from the prior art, for example, from DE 41 40 236 A1, DE-OS 25 41 841 or DE 10 2007 051 470 A1.
Here, a basic distinction is made between transverse leaf springs which impart a wheel-controlling action, that is to say transverse leaf springs which support occurring forces, and transverse leaf springs which do not impart a wheel-controlling action, that is to say transverse leaf springs which are mounted in a correspondingly flexible fashion. In particular, a distinction is made between transverse leaf springs which impart a wheel-controlling action laterally or which do not impart a wheel-controlling action laterally, and transverse leaf springs which impart a wheel-controlling action in the vehicle longitudinal direction and transverse leaf springs which do not impart a wheel-controlling action in the vehicle longitudinal direction, that is to say transverse leaf springs which support occurring transverse or lateral forces and are mounted in a flexible fashion in the vehicle transverse direction, and transverse leaf springs which support occurring longitudinal forces and are mounted in a flexible fashion in the vehicle longitudinal direction.
The expression “which impart a partial wheel-controlling action (laterally and/or in a longitudinal direction)” is used to refer to transverse leaf springs which accommodate or support only a part of the wheel-controlling forces acting laterally or in the longitudinal direction, and/or which support forces acting laterally or in the longitudinal direction only in certain driving situations. That is to say, a transverse leaf spring which imparts a partial wheel-controlling action (laterally and/or in a longitudinal direction) is mounted, in particular attached to the vehicle body and to the wheel suspension arrangement, such that, by the transverse leaf spring, only a part of the forces (lateral and/or longitudinal forces) can be supported, and/or the forces (lateral and/or longitudinal forces) can be supported only in certain driving situations.
The aforementioned DE 41 40 236 A1 and DE-OS 25 41 841 each disclose a transverse leaf spring axle for a two-track motor vehicle, which transverse leaf spring axle has a transverse leaf spring which imparts a wheel-controlling action laterally and in a longitudinal direction and which is supported at two mutually spaced-apart points on the vehicle body. Here, the transverse leaf spring is attached by its ends, that is to say at the wheel carrier side, in each case rigidly, in particular dimensionally rigidly, to a lower transverse link, that is to say the transverse leaf spring connects the left-hand lower transverse link to the right-hand lower transverse link.
It emerges from DE 10 2007 051 470 A1 that the support of the lateral forces on the vehicle body via the transverse leaf spring can be achieved, for example, by virtue of the transverse leaf spring being attached to the vehicle body, for the purposes of supporting the acting lateral forces, by two eccentric bearings which are approximately rigid in a vehicle transverse direction, and secondly being attached to or supported on the wheel carrier with such rigidity, for example, by a fixed screw connection by one or more screws or by a coupling element in the form of a correspondingly designed rubber bearing, so as to act similarly to a transverse link and thus impart a wheel-controlling action laterally. Owing to the rigid attachment of the leaf spring in the vehicle longitudinal direction, too, the leaf spring also imparts a wheel-controlling action in the longitudinal direction.
Such transverse leaf spring axles are in this case suitable in particular for axles which are constructed in accordance with the principle of a spring strut axle, in particular for axles which are constructed in accordance with the principle of a MacPherson spring strut axle, that is to say with damper struts which are supported in each case at the wheel side on the wheel carrier but which, instead of a spring strut, have only a damper strut, that is to say which have no helical spring arranged around the damper strut. In this case, the spring function can be performed by the transverse leaf spring. That is to say, the helical spring, which is commonly also referred to as a supporting spring, can be omitted.
The omission of the helical spring, however, basically has the disadvantage, in relation to a classic MacPherson spring strut axle, that the transverse forces acting on the damper strut owing to an occurring wheel load can no longer be compensated, because the transverse force compensation is generally achieved by virtue of the helical spring, along its longitudinal axis, also referred to as supporting spring axis, being inclined slightly obliquely relative to the damper axis, such that the damper piston, during compression and rebound movements, at least in certain driving situations, can be moved in the damper tube along the damper axis virtually without transverse forces and, as a result, with less friction than without transverse force compensation.
A further basic problem occurs in the case of axles with transverse leaf springs which impart an at least partial wheel-controlling action (laterally and/or in a longitudinal direction) and which are attached by their ends in each case in substantially rigid fashion to a lower transverse link. During the compression and/or rebound movement of the wheel, the articulated connection by which the transverse leaf spring is attached to the transverse link kinematically follows both the movement of the transverse leaf spring and that of the lower transverse link, even though the transverse link and the end of the transverse leaf spring actually move on different paths, because the transverse link and the transverse leaf spring rotate in each case about different attachment points. During the compression and rebound movements, the transverse link moves about its vehicle-body-side attachment point, and the transverse leaf spring rotates about the adjacently situated attachment point on the vehicle body, which does not coincide with the vehicle-body-side attachment point of the lower transverse link.
Since the transverse leaf spring is, however, rigidly connected to the transverse link and the rigidity of the transverse link in its longitudinal direction, that is to say over its length, is generally considerably greater than the rigidity of the transverse leaf spring, the forces that occur during compression and rebound movements generally result in a lengthening of the transverse leaf spring, such that the latter is forcibly guided along the path of the transverse link. This results in distortion of the transverse leaf spring, which is intensified with increasing compression or rebound travel because, with increasing compression and rebound travel, the actual path difference increases. For optimum driving behavior, it is, however, important that the transverse leaf spring can move as far as possible without distortion, in particular can bend as far as possible without distortion, during the compression and rebound movements. As a result, an axle in which the transverse leaf spring is rigidly attached to the lower transverse link for the purposes of supporting occurring lateral forces does not exhibit optimum bending behavior.
It is thus an object of the present invention to provide an axle having a transverse leaf spring, which imparts an at least partial wheel-controlling action laterally and/or in the vehicle longitudinal direction, for a two-track vehicle. It is also an object to provide a two-track vehicle having a corresponding axle, which firstly exhibits the most optimum possible bending behavior, that is to say whose transverse leaf spring is distorted to the least possible extent during compression and rebound movements, and which, in relation to the axles known from the prior art, permits improved compensation of the transverse forces which act on the damper strut and which increase the friction thereof.
This and other objects are achieved by an axle in accordance of embodiments of the invention and/or by a two-track motor vehicle having such an axle in accordance of embodiments of the invention. Advantageous and preferred embodiments of the invention are the subject of the claims and will be discussed in more detail below. The wording of the claims is incorporated by express reference into the content of the description.
An axle according to the invention is characterized in that the transverse leaf spring is attached by its wheel-carrier-side end region to the damper strut and is supported at a third effective kinematic point on the damper strut.
That is to say, in the case of an axle according to the invention, the left-hand damper strut and the right-hand damper strut are coupled to one another by the transverse leaf spring, in particular are connected to one another by the transverse leaf spring. The transverse leaf spring, which extends substantially in a vehicle transverse direction, that is to say in a y-direction, may in this case be formed in one piece over its length, that is to say may extend approximately from the left-hand wheel carrier to the right-hand wheel carrier, or may, in a manner known from the prior art, be of multi-part form, that is to say may be assembled from multiple transverse leaf spring parts in the vehicle transverse direction.
Here, an axle according to the invention is basically constructed in the manner of a spring strut axle, in particular in the manner of a MacPherson spring strut axle, but the helical springs arranged around the damper strut in the case of spring strut axles can be omitted. That is to say, an axle according to the invention preferably has only a damper strut on each side of the vehicle. As a result, such axles are generally less complex, and in many cases require less structural space than other spring strut axles. Furthermore, transverse leaf spring axles commonly have a weight advantage in relation to spring strut axles.
It is self-evidently also contemplated for an axle according to the invention to be provided with a spring strut on each side of the vehicle rather than a damper strut. However, for an optimum spring characteristic of an axle of said type, careful coordination of the individual spring elements with one another is necessary.
The transverse leaf spring of an axle according to the invention is in this case designed to impart an at least partial wheel-controlling action laterally and/or to impart an at least partial wheel-controlling action in the vehicle longitudinal direction. That is to say, by the transverse leaf spring of an axle according to the invention, at least a part of the lateral forces and/or at least a part of the longitudinal forces can be supported, and/or the lateral forces and/or the longitudinal forces can be supported in certain driving situations.
The transverse leaf spring may, however, also be designed to impart a wheel-controlling action laterally and/or to impart a wheel-controlling action in the vehicle longitudinal direction, that is to say such that all occurring lateral forces and/or all occurring longitudinal forces can be supported by the transverse leaf spring.
By the manner in which the transverse leaf spring can be attached to the vehicle body and the manner in which the transverse leaf spring is attached to the damper strut, that is to say the manner in which the corresponding attachments of the transverse leaf spring are configured, the transverse leaf spring acts as a transverse leaf spring which imparts a wheel-controlling action laterally and/or in the vehicle longitudinal direction or as a transverse leaf spring which imparts a partial wheel-controlling action laterally and/or in the vehicle longitudinal direction.
Here, an axle according to the invention may be formed either as a front axle or as a rear axle, wherein the axle may in each case be formed as a steerable or non-steerable axle.
If an axle according to the invention is formed as a steerable axle, the first and second kinematic points are preferably arranged so as to define a steering axis, that is to say the axis about which the wheel rotates during a steering movement.
The transverse leaf spring of an axle according to the invention may have one spring leaf or multiple spring leaves or one or more spring layers, wherein the transverse leaf spring preferably has multiple spring leaves arranged in particular parallel and one above the other, which spring leaves particularly preferably form a leaf spring pack. The transverse leaf spring is in this case preferably arranged such that, with regard to a functionally installed state in a vehicle, the spring leaves are arranged substantially one above the other in the vehicle vertical direction. That is to say, the individual spring leaves are preferably stacked approximately in a z-direction, preferably parallel and one above the other. The transverse leaf spring may, however, also be arranged in a slightly inclined manner, that is to say so as to be inclined slightly about the y-axis, such that bending of the transverse leaf spring is effected not only by vertical forces, but also by longitudinal forces, albeit preferably only to a much smaller extent.
The geometry of the individual spring leaves, in particular the shape thereof and the thickness and cross-sectional profile thereof in a vehicle transverse direction, is in this case preferably selected, and the leaf spring packs are preferably assembled in a coordinated fashion with respect to one another, such that the desired spring characteristic is obtained.
Here, the spring leaves may be produced from conventional spring steel, or else from fiber-reinforced plastic or the like. It is self-evidently also possible for a leaf spring pack, or the entire transverse leaf spring, to be assembled from multiple spring leaves composed of different materials.
With an axle according to the invention, it is firstly possible for transverse forces which act on the damper strut and which adversely affect the friction to be reduced in relation to transverse leaf spring axles known from the prior art, in which the transverse leaf spring is supported on the lower transverse link. Furthermore, as a result of the decoupling of the transverse leaf spring from the transverse link, in particular as a result of the attachment of the transverse leaf spring to the damper strut rather than to the transverse link, distortion of the transverse leaf spring during the compression and rebound movements can be avoided, even in the case of a transverse leaf spring which imparts a wheel-controlling action laterally and/or in the vehicle longitudinal direction.
In a preferred embodiment of the invention, the transverse leaf spring is attached by its wheel-carrier-side end region to the damper strut in the region of the damper tube, preferably in the region of a lower end of the damper tube or in the region of an upper end of the damper tube.
Since, in a functionally installed state in which the damper strut is attached by its upper end to the vehicle body, a transverse force which is exerted on the damper strut via the first kinematic point at which the damper strut is attached to the wheel carrier is supported both on the upper end of the damper piston and via the transverse leaf spring, the magnitude of the transverse force which acts on the damper piston and which increases the friction is dependent on the height or the position of the attachment of the transverse leaf spring to the damper strut. That is to say, what is of importance is at what height of the damper strut, that is to say where on the damper strut over its length, the third kinematic point, at which the transverse leaf spring is attached to the damper strut, is situated.
That is to say, depending on where the transverse leaf spring is attached to the damper strut, a transverse force acting on the damper strut is supported to a greater or lesser extent via the transverse leaf spring rather than via the damper piston, which is attached by its upper end to the vehicle body in a functionally installed state. The closer the third kinematic point is situated to the first kinematic point, the lower the transverse force acting on the damper piston, because a greater fraction can be supported by the transverse leaf spring, that is to say the better the transverse force compensation.
In a particularly preferred embodiment, in a vehicle vertical direction with regard to a functionally installed state of the axle in a motor vehicle, the transverse leaf spring is attached to the damper strut at the level of the first effective kinematic point, wherein preferably, the third kinematic point is situated at the height of the first kinematic point. In the case of such an attachment, the transverse force acting on the damper strut is supported virtually entirely by the transverse leaf spring, such that virtually no transverse force acts on the damper piston and an increase of the friction in the damper strut can be virtually avoided.
In particular, if the attachment of the transverse leaf spring to the damper strut at the height of the first kinematic point is not possible, for example because no structural space is available, it may be advantageous if the transverse leaf spring is attached under preload to the damper strut, and with regard to a functionally installed state of the axle in a motor vehicle, preferably under preload with a counter moment which acts about a vehicle longitudinal axis and which at least partially counteracts a transverse force generated owing to occurring wheel loads and directed toward the vehicle center and running through the first effective kinematic point and acting on the damper strut. With such a counter moment, a force component directed counter to the transverse force is generated at the attachment point of the damper piston, resulting in a lower resulting transverse force. With a correspondingly selected, defined preload, the transverse force can in certain situations even be completely compensated. The preload required for this purpose is in this case dependent, inter alia, on the position of the attachment point of the transverse leaf spring on the damper strut, that is to say on the arrangement of the third kinematic point.
In a preferred embodiment, the transverse leaf spring is articulately attached to the damper strut, particularly preferably by a joint. Here, the joint is preferably a ball joint or a rotary joint which permits an attachment under preload, in particular an attachment under preload with a counter moment which acts about a vehicle longitudinal axis and which at least partially counteracts a transverse force generated owing to occurring wheel loads and directed toward the vehicle center and running through the first effective kinematic point and acting on the damper strut.
The attachment of the transverse leaf spring to the damper strut is in this case designed in each case in accordance with the forces to be supported, that is to say such that the transverse leaf spring imparts an at least partial wheel-controlling action laterally and/or in the vehicle longitudinal direction.
In a particularly preferred refinement, the transverse leaf spring itself forms a joint, wherein, for this purpose, the wheel-carrier-side end region of the transverse leaf spring is in the form of a joint. For this purpose, the transverse leaf spring may, for example, be of angled design in its end region and mounted with its angled end on the damper strut such that, in the region, the transverse leaf spring forms a type of hinge joint. With a transverse leaf spring of this type or an attachment of this type, the transverse leaf spring can be attached under preload to the damper strut particularly easily. Alternatively, it is, however, self-evidently also possible for a separate hinge joint or the like to be used.
Alternatively or in addition, the transverse force acting on the damper piston can be reduced by virtue of the damper strut being attached by the damper tube under preload to the wheel carrier, and with regard to a functionally installed state of the axle in a motor vehicle, preferably under preload with a counter moment which acts about a vehicle longitudinal axis and which at least partially counteracts a transverse force generated owing to occurring wheel loads and directed toward the vehicle center and running through the first effective kinematic point and acting on the damper strut. This type of attachment of the damper strut under a corresponding preload to the wheel carrier has the advantage that the damper does not introduce into it any force which has to be supported as completely as possible by the transverse leaf spring or which has to be compensated by a corresponding preload in the attachment of the transverse leaf spring to the damper strut.
As mentioned in the introduction, an axle according to the invention has a transverse leaf spring which imparts an at least partial wheel-controlling action laterally and/or in the vehicle longitudinal direction. The manner in which the transverse leaf spring can be attached to the vehicle body and the manner in which the transverse leaf spring is attached to the damper strut, that is to say the manner in which the corresponding attachments of the transverse leaf spring are designed, determines whether the transverse leaf spring acts as a transverse leaf spring which imparts a wheel-controlling action laterally and/or in the vehicle longitudinal direction or as a transverse leaf spring which imparts a partial wheel-controlling action laterally and/or in the vehicle longitudinal direction.
Since, for the best possible harmonic spring characteristic in the vehicle transverse direction, the transverse leaf spring itself should be attached in as flexible a manner as possible at least within certain defined limits, that is to say in such a way that a lateral compensation movement or a lateral displacement of the transverse leaf spring in the y-direction is possible, which opposes support of occurring lateral forces, it may in some cases be necessary for additional measures to be provided which firstly permit the lateral displacement of the transverse leaf spring within certain defined limits, such as is necessary for a good spring characteristic, but which at the same time permit support of occurring lateral forces via the transverse leaf spring at least in certain driving situations.
In this case, what has proven to be particularly advantageous is an axle according to the invention which has in each case one wheel carrier and one damper strut on each side of the vehicle and one Watt linkage which is coupled to the transverse leaf spring and which can be coupled to the vehicle body. The two damper struts are coupled to one another by the transverse leaf spring, and the transverse leaf spring can be attached by at least one bearing to the vehicle body. Here, the bearing is designed for supporting the transverse leaf spring in a vehicle vertical direction and simultaneously permits a compensation of a movement of the transverse leaf spring in a vehicle transverse direction during compression and/or rebound movements. The Watt linkage is designed, coupled to the transverse leaf spring, and capable of being coupled to the vehicle body, such that, in a functionally installed state of the axle in a two-track motor vehicle, the Watt linkage prevents a movement of the transverse leaf springs in the vehicle transverse direction caused by forces acting on the transverse leaf springs, or limits the movement to a defined maximum admissible transverse movement.
A Watt linkage of this type is described in detail in DE 10 2014 223 600.2 (EM27932), filed by the same applicant on the same date, which is hereby expressly incorporated in its entirety into the content of this description.
If the Watt linkage is designed to be coupled to the transverse leaf spring and to be coupleable to the vehicle body so as to prevent a global movement of the transverse leaf spring in the vehicle transverse direction, the axle, in particular the Watt linkage, is preferably designed such that lateral forces acting on the transverse leaf spring are supported on the vehicle body. That is to say, in this case, the transverse leaf spring imparts a wheel-controlling action laterally and supports lateral forces, which are introduced into the axle via the wheels, virtually entirely on the vehicle body, and a global transverse movement, and thus the displacement of the entire transverse leaf spring in the vehicle transverse direction, is virtually entirely blocked by the Watt linkage. Only the bearing, by which the transverse leaf spring is supported directly on the vehicle body, permits a small compensation movement in the vehicle transverse direction within the bearing in order to permit bending of the transverse leaf spring as far as possible without distortion during compression and rebound movements.
By contrast, if the Watt linkage is designed to be coupled to the transverse leaf spring and to be coupleable to the vehicle body so as to limit a global movement of the transverse leaf spring in the vehicle transverse direction to a defined maximum admissible transverse movement, the axle, in particular the Watt linkage, is preferably designed such that, after the defined maximum admissible transverse movement of the transverse leaf spring is reached, lateral forces acting on the transverse leaf spring are supported on the vehicle body. In this case, the transverse leaf spring imparts only a partial wheel-controlling action laterally, in particular only when the maximum admissible transverse movement of the transverse leaf spring has been reached.
In this case, the transverse leaf spring may preferably be attached to the vehicle body such that, in a functionally installed state of the axle in a two-track motor vehicle, adequate displaceability in the y-direction is ensured, preferably such that the spring action of the transverse leaf spring is not impeded, wherein, for this purpose, the transverse leaf spring may be attached by at least one bearing to the vehicle body.
The bearing for coupling the transverse leaf spring to the vehicle body should in this case, in order to achieve the correspondingly desired spring action, be designed for supporting the transverse leaf spring in the vehicle vertical direction and permit compensation of a movement of the transverse leaf spring in the vehicle transverse direction during compression and/or rebound movements.
Depending on whether it is intended for longitudinal forces to be supported, that is to say whether the transverse leaf spring is intended to impart a wheel-controlling action in the longitudinal direction, or whether flexibility in the vehicle longitudinal direction, that is to say in the x-direction, is desired, the transverse leaf spring of an axle according to the invention may be attached to the vehicle body rigidly or with corresponding flexibility in the vehicle longitudinal direction.
Such bearings which permit compensation of a movement of the transverse leaf spring in the vehicle transverse direction during compression and/or rebound movements while simultaneously providing support in the vehicle vertical direction, possibly with corresponding flexibility or rigidity in the x-direction, are basically known from the prior art.
However, the bearings described in DE 10 2014 223 576.6 (EM28004), filed on the same date by the same applicant, have proven to be particularly suitable for the attachment of the transverse leaf spring of an axle according to the invention to the vehicle body. DE 10 2014 223 576.6 (EM28004) is hereby incorporated by express reference, in its entirety, into the content of the description.
The bearings described in DE 10 2014 223 584.7 (EM28029), likewise filed on the same date by the same applicant, have likewise proven to be particularly suitable for the attachment of the transverse leaf spring of an axle according to the invention to the vehicle body, wherein DE 10 2014 223 584.7 (EM28029) is hereby likewise incorporated by express reference, in its entirety, into the content of the description.
It is, however, preferably possible for the transverse leaf spring to be coupled to the vehicle body not only by a single bearing as described above, but by at least two such bearings, in particular two eccentrically arranged bearings, preferably by two bearings offset outward symmetrically with respect to the vehicle center. This type of attachment of a transverse leaf spring to the vehicle body, such as is basically known from the prior art, has the advantage that the transverse leaf spring simultaneously acts as a transverse stabilizer during a rolling movement. In this way, wheel load differences between the left-hand wheel and the right-hand wheel can be reduced, and the lateral force control potential of the axle can be increased in relation to an axle with only one transverse leaf spring bearing. It is self-evidently also possible, as is likewise known from the prior art, for two eccentric bearing pairs to be provided.
A two-track motor vehicle according to the invention is characterized in that it has an axle according to the invention.
The individual features may be realized in each case individually or severally in the form of sub-combinations in an embodiment of the invention and can form advantageous, independently patentable embodiments, for which protection is hereby claimed. All of the features and feature combinations mentioned above in the description and below in the description of the figures in conjunction with an axle according to the invention and/or shown in the figures alone apply in each case not only to the axle according to the invention, but also to a two-track motor vehicle according to the invention, and may be used in each case not only in the described feature combinations but also in other technically feasible combinations or individually.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.